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Atmospheric Limits: A Review of the Effect of Path Length Variations on the Coherence and Accuracy of VLBI

Published online by Cambridge University Press:  03 August 2017

Alan E.E. Rogers
Alan E.E. Rogers*
Affiliation:
Haystack Observatory, Westford, MA 01886

Abstract

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Interferometer phase fluctuations produced by path length variations in the troposphere limit the coherence to between 100 and 1000 seconds at a 3 millimeter wavelength. An expression for the coherence is given using an Allan variance to characterize the atmospheric phase fluctuations. Methods of optimizing the fringe detection threshold and calibrating the fringe visibilities under poor conditions of poor coherence are outlined. The astrometric and geodetic accuracy of VLBI is limited by our ability to calibrate the atmospheric path. Atmospheric “self-calibration” techniques which use the elevation dependence of interferometer delay to solve for the highly variable “wet” component of troposphere are discussed. Various models for the elevation dependence of atmospheric path or “mapping function” are reviewed. The accuracy limits imposed by the atmosphere are discussed.

Type
Instrumentation and Analysis
Information
Symposium - International Astronomical Union , Volume 129: The Impact of VLBI on Astrophysics and Geophysics , 1988 , pp. 533 - 541
Copyright
Copyright © Reidel 1988 

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